Glossary of NCAR Graphics terms
Definitions that are specific to a particular part of the package are
prefaced accordingly. For example, definitions that apply only to NCL
are prefaced with NCL: .
A,
B,
C,
D,
E,
F,
G,
H,
I,
J,
K,
L,
M,
N,
O,
P,
Q,
R,
S,
T,
U,
V,
W,
X,
Y,
Z
- annotation
- A viewable object whose
location and usually size are set relative to the viewport or data coordinate space of a
base plot.
There are three kinds of annotations:
intrinsic annotations,
embedded annotations,
and external annotations.
- annotation functions
- The functions used to add and remove annotations
to and from plot objects. Specifically,
these functions are
NhlAddAnnotation and
NhlRemoveAnnotation
for the C and Fortran interfaces.
- annotation plot
- An annotation that is a
plot object and not simply a
viewable object. An annotation plot
is a subordinate base plot.
- ANSI
- The American National Standards Institute, an independent non-profit
organization that creates and publishes U.S. national standards
(such as Fortran, C, CGM, and so forth) taking input from all sectors
of the technical community and the public at large. ANSI also works
in collaboration with other standards organizations such as
ISO
(the International Standards Organization) and IEEE (the Institute
of Electrical and Electronics Engineers).
- API
-
Application Programming Interface.
- application
- A program written in C, Fortran, or
NCL that utilizes any of the functionality of NCAR Graphics.
- application class
- Refers specifically to the class
App. Objects that
are instances of this class are used to keep
track of resource databases. Every application must create at least one
App object (this will be done automatically for you if you use
NhlOpen).
-
Application Programming Interface
- The programming interfaces (C, Fortran, and
NCL) to the NCAR Graphics
package. These interfaces provide access to the support functions
defined in the classes as well as provide additional useful
functionality.
- application resource file
- A resource file that is specific to a particular application.
There are two application-specific resource files: a system
application-specific resource file and a user application-specific
resource file. The user can specify what directories the
application-specific resource files are in. By default, the
user application-specific resource file is in the local current
directory and the system application-specific resource file is in
the directory specified by the setting of the environment variable
NCARG_SYSAPPRES.
Resources defined in the user application-specific
resource file will override resources defined in the system
application resource file.
- area fill pattern
- A pattern to use for filling a polygonal area. The patterns are
selected by using an integer fill index into a table of patterns.
- ASCII
- Stands for "American Standard Code for Information Interchange."
This is an ANSI Standard specifying a set of 128 characters with
their associated coded integer representations.
- ASCII file
- NCL: A data file that contains integers or floating point
data values in ASCII format.
- aspect ratio
- Specifies the height-to-width ratio of a plot. This term
is also applied to characters. For example, characters
with an aspect ratio of 2.0 are twice as tall as they are wide.
- associative operator
- A binary operator that obeys the law of associativity: i.e. a
binary operator "R" such that (aRb)Rc = aR(bRc) for all legal
operands a, b, and c.
- attribute
- NCL: A singly-dimensioned datum of any type that
is assigned to a variable using the ' @ ' operator. An attribute
of a variable contains descriptive information about the variable.
- background color
- The color that will be used as a background color for the entire
viewable surface of a physical workstation when plots are drawn on it.
- base plot
- A plot object responsible for setting
the viewport of zero or more
plot members relative to its own viewport.
There are two kinds of base plot:
primary base plots and
subordinate base plots.
At creation, any plot object is a primary base plot.
A plot object ceases to be a base plot when added to another plot
object as an overlay. When added as an
annotation a plot object becomes a
subordinate base plot. A plot object must be a primary
base plot for users to draw it or change its workstation.
- binary file
- NCL: A data file that contains integer or
floating point data stored in a format not supported by NCL.
- bounding box
- For View class objects,
the bounding box for such objects is the
smallest rectangle in NDC space that contains all of the marks
that would appear on an output workstation if the object were drawn.
- CGM
- Computer Graphics Metafile.
- child
- A relationship that holds between objects. If "A" and "B"
are objects, then B is a child of A provided that when B was
created, A was specified as being its parent (either in the
fourth argument of an NhlCreate call, or in a NCL create
expression), or B was made a child of A by using the
NhlChangeWorkstation function. If B is a child of A, then the
following conditions apply:
- B inherits the resource database of A. If viewable, B will
display to the same workstation as A; if A is a
workstation, then B will draw to A.
- Destroying A will destroy B.
- Resources can be specified in resource files
as: {App obj name} . {parent of A} . {Name of A} .
{Name of B} . {resource of B} : {value}.
-
- A child can have only one parent. See also parent.
- child/parent hierarchy
- The tree structure determined by the child/parent relationship
existing among all current objects in an application. A child can
have only a single parent, but a parent may have many children.
The child/parent hierarchy should not be confused with the class
hierarchy. See also class hierarchy.
- class
- A template for defining objects that specifies variables, and
procedures that operate on those variables. In the context of the
NCAR HLU library, the class variables are called resources and the
class procedures are called support functions. Objects are members,
or instances, of a class formed by assigning specific values to
the variables in the class.
- class hierarchy
- Each class, except the base class, is derived from some other class.
The tree structure determined by the derived-class/superclass
relationships among all of the classes is called the class hierarchy.
The class hierarchy should not be confused with
the child/parent hierarchy.
- color index
- See color table.
- color map
- Same as color table.
- color table
- A table that associates integer values (called color indices)
with RGB color values. In NCAR Graphics, color tables contain
up to a maximum of 256 colors (including the background color).
- command
- NCL: Same as an NCL statement.
- composite class
- A class that combines the resources of other classes with its own.
A composite class inherits resources and functions from its
superclass and it shares the resources from its composite members
by the process of resource forwarding. If the composite class
members have support functions, these functions do not apply to
the composite class.
- composite class member
- A class used as part of the functionality
of a composite class.
- composite class resource
- A resource available to a composite class by way of resource
forwarding from a member class of the composite class.
- Computer Graphics Metafile
- A graphics metafile is a file that contains encoded vector graphics
elements such as lines, colors, dash patterns, markers, and so
forth. The Computer Graphics Metafile (CGM) is a
precisely-defined formatting for a graphics metafile as defined and
standardized by ANSI. NCAR Graphics produces
a version of the CGM
that is called a conforming private encoding that can easily
be converted to and from standard CGM by using the filters ncgm2cgm
and cgm2ncgm. The NCAR private encoding is also called NCAR CGM, or NCGM.
- coordinate variable
- NCL: A value associated with a named dimension of a variable
or file variable that contains numerical coordinate information for
each index of the dimension. Coordinate variables must be singly-
dimensioned values. Warnings are produced if the array of values
assigned is not monotonically increasing or decreasing.
- ctrans
- The NCGM interpreter distributed with NCAR
graphics.
- dash pattern
- A pattern (such as "solid", "dotted", and so forth) to use as a
line style when lines are plotted using the
draw function.
Dash patterns are selected by using an integer index into a table
of dash patterns.
- data classes
- Any of the classes that are used to provide user input data to any
of the objects that utilize such data. These classes are the
CoordArrays class,
the CoordArrTable class,
and the ScalarField class.
- data conversion
- The process of converting data stored in one format to another
format, such as converting data stored as integers to data stored
as floating point numbers. Some objects, such as ScalarField, perform
automatic data conversions.
- data coordinate space
- The coordinate space that is appropriate to input data.
Transformations can be effected between data coordinate space and NDC
(see
Normalized Device Coordinates).
- data specific resource
- A resource of a particular
class, such as the XyPlot class, that can be used
to modify the attributes of data supplied via a
DataSpec object.
Data specific resources can be used to control attributes such as
curve colors, dash patterns, marker sizes, marker colors, and so forth.
- data transformation
- A process that transforms data from one coordinate space to
another, such as transforming data in logarithmic space to data
in linear space.
- data type
- NCL: A data type is a representation of data
that defines a size and valid range for numerical data or
provides a reference to a file or HLU graphical object.
- derived class
- See subclass.
- drawable object
- See viewable object.
- draw function
- Specifically, either the
NhlDraw
function of the C or Fortran interfaces, or the
draw function of NCL, that is invoked to plot a
View object.
- embedded annotation
- An annotation that may be
incorporated as part of the functionality of subclasses of the
Transform class. It is managed
internally by the controlling
PlotManager.
- Encapsulated PostScript
- Encapsulated PostScript (EPS) is a subset of regular
PostScript. The
restrictions placed on EPS files are for making it an appropriate
format for importing into applications that import PostScript.
-
Encapsulated PostScript Interchange Format
- Encapsulated PostScript Interchange Format (EPSI) files are
Encapsulated PostScript files
that have a "preview bitmap" that represents the PostScript
image contained in the file. The bitmap (and it is a bitmap and
not a color map) can be used by an importing application to quickly
display a picture of the imported file.
- EPS
- see Encapsulated PostScript
- EPSI
- see
Encapsulated PostScript Interchange Format
- error class
- A class that is used to configure the error reporting module of the
HLU library. For any application, there is precisely one
error object
created, and it is created automatically for you. The error
class defines several resources for controlling error reporting.
- expression
- NCL: Any sequence of NCL operators and operands that results
in the computation of a value. In particular, any literal value is
an expression and any variable is an expression. Also, arrays are
expressions as well as functions. Operators applied
to expressions are expressions.
- external annotation
- An annotation consisting of an
arbitrary user-created viewable
object added to a plot object.
The user controls the location and size relative to the
base plot by manipulating the resources
of a user-accessible
AnnoManager object.
- file
- NCL: A data file residing external to NCL in one of NCL's
supported data formats.
- file variable
- NCL: A variable, created by the NCL
addfile
function, that contains a reference to a file.
- fill value
- NCL: Same as missing value.
- fontcap
- A file that contains detailed information used to plot characters.
Fontcaps have a human-readable ASCII form and a binary form that is
readable by ctrans.
- foreground color
- The color associated with color index 1. This is used as the
default color in drawing viewable objects.
- function
- HLU:
Any member of the
HLU API.
NCL:
An identifier with a list of parameters separated by commas and
enclosed in parentheses. Functions return values when called.
A function is defined by NCL source unlike the NCL
intrinsic function.
- GIF
- A file format used for the storage and on-line retrieval of
bitmapped graphical data. GIF stands for "Graphical Interchange
Format"; it was created by the CompuServe Corporation in 1987.
- graphcap
- A file that contains detailed information used to define the
capabilities of a specific plotting device. Graphcaps have a
human-readable ASCII form or a binary form
that is readable by ctrans.
- graphical object
- NCL: An NCL value of type graphic. A graphical object is an
identifier for an
HLU object.
- Graphical User Interface
- A non-programmatic, graphical, interface to the functionality
of NCAR Graphics. Such an interface is sometimes referred to as
a "point-and-click" interface, since that is how the interaction
is accomplished.
- GUI
- Graphical User Interface.
- HDF
-
HDF (Hierarchical Data Format) is a multi-object file format,
developed at NCSA, that facilitates the transfer of various types
of data between machines and operating systems.
- High Level Utilities
- Objects, like XyPlot objects, Contour objects, TextItem objects, and
so forth, that can be created and manipulated by a set of library
functions, callable from either a C program, a Fortran program,
the NCAR Command Language, or a GUI. High Level Utilities are
also referred to as HLUs and are to be distinguished from the
Low Level Utilities, or LLUs.
- HLU resource string
- A character string identifying a particular resource of a class.
These are the resources listed in the descriptions of the classes.
- HLUs
- High Level Utilities.
- identifier
- NCL: A name of a
variable, or a
function, or a
procedure.
- immediate mode
- A mode used by certain
API
functions that produces immediate drawing without invoking a
draw function.
- instance
- When specific values are assigned to all the resources defined in
a class, the result is an instance of that class. Any instance of
any class is called an object. Default values
exist for all resources; before creating an object, users may override
any default value.
- instance hierarchy
- Same as child/parent hierarchy.
- inheritance
- A class is said to inherit resources or support functions from
its superclasses, since those functions and resources are available
to the subclass.
See superclass, and
composite class.
- intrinsic annotation
- An annotation available as composite class member of the
PlotManager class.
Intrinsic annotations are available to any class of
plot object and include
TickMark,
Title,
LabelBar, and
Legend annotations. The
PlotManager manages these annotations internally.
- intrinsic function
- NCL: An identifier with a list of parameters, the
parameters being separated by commas enclosed and
in parentheses. Intrinsic functions return values when called.
An intrinsic function is not defined by NCL source; it is a C or Fortran
routine that has been added to the NCL function set.
Intrinsic functions often perform operations that NCL source
does not support.
- ISO
- The International Standards Organization that publishes international
standards.
(see ANSI).
- intrinsic procedure
- NCL: An identifier with a list of parameters, the parameters
being separated by commas enclosed
in parentheses. An intrinsic procedure is not defined by NCL
source; it is a C or Fortran routine that has been added to the
NCL procedure set. Intrinsic procedures often perform operations that
NCL source does not support.
- keyword
- NCL: A word reserved by NCL that not allowed to be used as a
variable or function name.
- lazy evaluation
- NCL: The process whereby relational expressions
are assigned a value
as soon as it is possible to do so, without necessarily evaluating
all of the components in the expression. For example, the expression
(1 .lt. 3) .or. (2 .lt. 1) can be assigned the value True immediately
after evaluating (1 .lt. 3) without having to evaluate (2 .lt. 1).
- literal array
- NCL: An array of values specified using literal values,
these values being separated by commas and enclosed in
' (/ ' and ' /) ' .
- literal value
- NCL: A single scalar value expressed by its actual string
value (i.e. not referenced by a variable). For example,
1, 1.414 and "string" are literal values.
- LLUs
- Low Level Utilities.
- local resources,
- Resources defined in a particular class that are not inherited
from another class.
- Low Level Utilities
- Traditional NCAR Graphics as it existed before Version 4.0. It is
a package of about 500 graphics routines. User entries have both C
and Fortran interfaces. These entries continue to be
supported in 4.0.
- marker
- See polymarker.
- member class
- One of the class components of a
composite class.
- metadata
- NCL: Information used to describe data, such as dimension
names, variable attributes, valid ranges, and so forth.
- metafile
- A file containing encoded graphical elements. Metafiles are used
for storing and transporting graphics images. In the context of
NCAR Graphics "metafile" is generally synonymous with
NCGM.
- missing value
- NCL: A special value for a variable or array element indicating
that no legal data has been specified for that quantity. See the
section on missing data in the evaluation of expressions in the
NCL User Guide module on
NCL expressions
and operators for details on how these missing values are
handled.
- monotone
- A sequence of numeric values is monotone (or monotonic) if either:
each element in the sequence is larger than (or equal to) its
predecessor, or each element in the sequence is smaller than
(or equal to) its predecessor. A sequence is monotonically increasing
if each element in the sequence is larger than its predecessor;
a sequence is monotonically decreasing if each element in the sequence
is smaller than its predecessor. A sequence is monotonically
non-decreasing if each element in the sequence is larger than,
or equal to, its predecessor. A sequence is monotonically
non-increasing if each element in the sequence is smaller than,
or equal to, its predecessor.
- named dimension
- NCL: A dimension of a variable or file variable that has been
assigned a name using the '!' operator.
- NCAR Command Language
- A language written for the purpose of interactive data manipulation
and display. NCL has a command line interface and will accept
netCDF, HDF, Grib, or ASCII input files. NCL also provides an
easy interface to the HLUs.
-
NCAR Computer Graphics Metafile
- The NCAR private binary encoding of a
Computer Graphics Metafile.
- NCGM
- NCAR Computer Graphics Metafile.
- NCL
- NCAR Command Language.
- NCL resource list
- NCL: An NCL resource list is a list of
HLU resource strings
followed by a " : " followed by a valid NCL
expression.
- NDC
- Normalized Device Coordinates. A coordinate system that describes
positions on a virtual plotting device. The lower left corner
corresponds to (0,0), and the upper right corner corresponds to
(1,1). NDC space will be mapped onto the largest
square which will fit on an actual plotting device.
PostScript output
is centered on the page by default, but options exist for
positioning PostScript output anywhere on the page. See the
PSWorkstation for details.
- netCDF
-
netCDF (network Common Data Form) is an interface for scientific
data access and a library that provides an implementation of the
interface.
- numeric
- NCL: Any data type that represents a numerical value. The numeric
data types are: double, float, long, integer, short, and byte.
- object
- An object is created from a class by assigning specific values for
the class resources. See class and
instance.
- overlay
- A transform overlaid on a
base plot using the
add overlay function.
The base plot sets the viewport of the overlay
to match its own and transforms the coordinate data of the overlay
into its own coordinate space. Only that portion of the overlay's
coordinate space that intersects the coordinate space of the
managing plot will be visible in the plot output. If the
overlay is a plot object, it gives up
its base plot status. The base plot to which the overlay is added
assumes responsibility for managing the overlay's
plot members.
- overlay functions
- The functions used to add and remove overlays
to and from plot objects. Specifically,
these functions are
NhlAddOverlay and
NhlRemoveOverlay
for the C and Fortran interfaces.
- overlay plot
- An overlay created from a
plot object rather than from a
simple transform.
- overlay sequence
- The ordering of the transforms in a
plot or subplot
that contains overlays.
The base plot is
always first, followed by each overlay in an order that may be
manipulated through the
overlay functions. The overlay sequence
determines the basic drawing order of the plot. The base plot is
drawn first; each succeeding overlay is drawn on top of the preceeding
transforms. Annotations are not affected by the overlay sequence; they
always drawn after all the transforms.
- parent
- A relationship that exists between objects. If A and B
are objects, then A is a parent of B if and only if B is a
child of A. See child for more information.
- polymarker
- An array of coordinates specifying positions where certain specified
symmetric symbols (markers) such as circles, dots, and so
forth will be plotted.
- plot
- Depending on context, the word plot may be used to mean:
- A plot object.
- A primary base plot and all its
plot members.
- The output resulting from drawing a primary base plot and
all its plot members.
- The output resulting from drawing any arbitrary collection
of viewable objects.
- plot_class
- NCL: The plot_class in NCL is the same as the HLU class
pointer used in the
HLU API to specify what type of object to create.
The NCL plot_class identifier is spelled the same as the
HLU class pointer.
- plot member
- A viewable object managed by a
base plot. If the base plot is
a subordinate base plot then the
object is indirectly a plot member of the complete plot
managed by the primary base plot.
Drawing the primary base plot
causes all its plot members to be drawn. A plot member is either an
overlay or an
annotation. Although an annotation can be
any arbitrary view , an overlay must be a view
belonging to the Transform class.
A plot member must belong to the same
Workstation as its base plot and cannot
be drawn independently. A view cannot belong as a plot member
to more than one base plot at a time.
- plot object
- A Transform object instantiated
with an active PlotManager.
In general, unless otherwise restricted
by their specific class, plot objects have the ability both to
manage other viewable objects as
plot members and to be managed as plot members
themselves. A plot object that manages plot members is called a
base plot. If the managing
plot object is itself managed as a plot member, it is a
subordinate base plot. If it
manages itself (i.e. is not a plot member) it is a
primary base plot. At creation,
all plot objects are primary base plots.
- PostScript
- A general-purpose programming language that contains a rich set
of graphics operators. PostScript is produced by many popular word
processing and graphics packages and can be displayed on a wide
variety of printers, plotters, and workstation screens.
- primary base plot
- A self-managing plot object. A
base plot that directly manages any number of
plot members, consisting of
overlays and
annotations, but is not itself a
plot member. At creation all plot objects are primary base plots.
A plot object must be a primary base plot for the user to
draw it or change its workstation.
- procedure
- NCL: An identifier with a list of parameters,
these parameters being separated by commas and enclosed
in parentheses. Procedures do not return values when called.
- PS
- see PostScript
- resource
- A variable defined as part of the definition of a class.
Resource values in objects
can be set by using a
Create function or
a SetValues function.
Resource values can be retrieved using a
GetValues function.
- resource file
- A file that can be used to set values for resources. There are four
different resource files. See system
resource file and
user resource file.
- resource forwarding
- A technique that makes the resources of
member classes available to
a composite class.
- RGB
- Stands for the red, green, blue color space where colors
are specified as triples of floating point numbers between 0. and 1.
inclusive. The number triple gives the intensities for the red,
green, and blue components of a color. The triple
<1,.0.,0.> would indicate red, for example.
- scalar
- NCL: A single element of data of any type is referred
to as a scalar value.
- scalar_logical_expression
- NCL: A single element value of the logical data type with
no missing values.
- scope
- NCL: The range or area within a program in which an identifier
is meaningful.
- subordinate base plot
- A plot member that is an
annotation plot. A subordinate base
plot sets the viewport of the
plot members it controls,
while its own viewport is set by the base plot
that controls it. Unlike a
primary base plot, the user cannot
directly draw or change the workstation of a subordinate base plot.
A subordinate base plot and the plot members it manages are
known collectively as a subplot.
- simple overlay
- An overlay created from a
simple transform.
- simple transform
- A transform object created without
an active PlotManager.
Unlike a plot object,
a simple transform cannot manage any
plot members, either as
annotations or as
overlays. Therefore, the only elements that
appear when a simple transform is drawn are those implemented
within the object itself. However, unless restricted by its
particular class, a simple transform may itself become an annotation
or an overlay of a base plot.
Since a plot object has all the capabilities of a simple transform
and none of the limitations, the main reason for creating a simple
transform would be to conserve system resources when PlotManager
capabilities are not required.
- statement list
- NCL: A sequence of statements separated by a carriage returns (\n).
- statement
- NCL: A single language construct within NCL that
performs a specific task.
- subclass
- A class B is a subclass of A if B has in it all of the
resources and support functions of A (B may have additional resources
and support functions as well). If B is a class derived from A,
then B is said to inherit its resources and support functions
from A. If B is derived from A, then it is also said that B
is a subclass of A.
- subplot
- The portion of a plot that is managed by a
subordinate base plot.
- superclass
- A class A is a superclass of class B if A is on the same branch of
the class hierarchy tree and A is higher on that branch.
- superclass resource
- A resource that one class inherits from a superclass.
- support function
- A function defined as part of a class definition.
- system resource file
- There are four files where resources can be set - two of these files
are system resource files and the other two are user resource
files. The name of one of the system resource files is specified by
the setting of the environment variable NCARG_SYSRESFILE; the
other system resource file is specified in an
application-specific manner. See
application resource file.
- transform
- A Transform object.
- Transform class
- The Transform class is
a subclass of the View class that supports transformations from
data coordinate space into the
NDC space occupied by the Transform class instance's
viewport. Transform subclasses may include
the PlotManager class as a
composite class member. The
Transform class provides a resource for activating or deactivating
the PlotManager when a Transform instance is created. In addition,
the Transform class provides support functions for converting
between data coordinate space and NDC space, for drawing
immediate mode graphics primitives, and
for adding and removing overlays and
annotations from
plot objects.
- Transform object
- An object that is an instance of the
Transform class. Transform objects
become plot objects when created with
an active PlotManager
instance. A Transform object created without an active PlotManager
is called a simple transform.
- user resource file
- There are four files where resources can be set - two of these files
are user resource files and the other two are system resource
files. The name of one of the user resource files is specified by
the setting of the environment variable NCARG_USRRESFILE; the other
user resource file is specified in an application-specific
manner. See application resource
file.
- variable
- NCL: A name that can contain a singly-dimensioned or
multi-dimensioned data array, dimension names, coordinate variables,
attributes, and so forth.
- view
- A viewable object.
- viewable object
- An object that is an instance of the View class.
- View class
- An object can be drawn only if it is an instance of the
View class. The View class provides resources for sizing and
positioning objects on an output device
(workstation). The View class also
provides a support function for determining the
bounding box of a given object in the class.
A View class object must have a
Workstation class parent.
- View object
- A viewable object.
- viewport
- For View objects, the viewport is a rectangular
subregion of NDC space that
specifies where the View object will be placed when
drawn. The precise meaning of the viewport depends on the
View object. For example, for XyPlot objects, the viewport
specifies where the grid containing the curves will be placed,
and the labeling (if any) will be drawn outside of the
viewport. On the other hand, for TextItem objects, the viewport will
be a rectangle surrounding the text string.
- visualization block
- NCL: A group of NCL resources
specified in either an NCL
create,
setvalues, or
getvalues
statement. Visualization blocks
are used to create, modify, or inquire about the values of
resources of objects.
- workstation
- Used in NCAR Graphics Version 4 terminology to mean a
valid output device such as an X Window System display, a
PostScript file, or an NCGM.
- workstation class
- A class that provides interfaces to specific output devices.
NCAR Graphics 4.1 Control Panel
NG 4.1 Home, Index, Examples, Glossary, Feedback, NG4.1 Contents, NG4.1 WhereAmI?
$Revision: 1.27 $ $Date: 1998/06/15 20:41:19 $